This section provides background information related to the present disclosure which is not necessarily prior art.
The state of blood vessels can be used as an index for diseases of an organ. For example, the state of pulmonary vessels has emerged as an meaningful index for many lung diseases, such as pulmonary hypertension, interstitial lung disease and chronic obstructive pulmonary disease (COPD) (see the paper by M. G. Linguraru et al., “Segmentation and quantification of pulmonary artery for noninvasive CT assessment of sickle cell secondary pulmonary hypertension,” Medical Physics, vol. 37(4), pp. 1522-1532, 2010).
The state of pulmonary vessels, particularly the result of the analysis of the distribution and scale of small pulmonary vessels, is one of the meaningful evaluation indices for the state of a pulmonary circulation state, and is essential for the analysis of various lung diseases.
Recent research shows that there are relationships between the measurable morphological characteristics of pulmonary vessels, such as diameters and an area percentage estimated from computerized tomography (CT) images, and various clinical parameters.
Various researches suggest that there is a close relationship between endothelial dysfunction, asserted to be related to pulmonary emphysema, and vascular alteration (see the paper by Santos et al., “Enhanced expression of vascular endothelial growth factor in pulmonary arteries of smokers and patients with moderate chronic obstructive pulmonary disease,” American Journal of Respiratory and Critical Care Medicine, vol. 167, pp. 1250-1256, 2003).
From the technological point of view, an attempt has been made to measure the morphological characteristics of large blood vessels using vascular contrast enhanced images (see the paper by Barrier et al., “Today's and tomorrow's imaging and circulating biomarkers for pulmonary arterial hypertension,” Cellular and Molecular Life Sciences, vol. 69, pp. 2805-2831, 2012).
However, there has rarely been an attempt to evaluate the morphological characteristics of small vessels.
Meanwhile, an attempt was made to perform simple thresholding in a two-dimensional (2D) sectional CT image in order to quantify pulmonary vessels, select circular regions having an area smaller than 5 mm2 as blood vessels, and show a correlation between the small areas of pulmonary vessels and a pulmonary function test (PFT) (see the paper by Matsuoka et al., “Quantitative computed tomographic measurement of a cross-sectional area of a small pulmonary vessel in nonsmokers without airflow limitation,” Japanese Journal of Radiology, vol. 29, pp. 251-255, 2011).
However, although the paper (by Matsuoka et al.) shows a strong clinical relationship between the distribution of blood vessels and a PFT, a pulmonary artery and a pulmonary vein are not distinguished from each other, it is difficult to accurately measure the diameter of a blood vessel in a direction orthogonal to the axis of the blood vessel because 2D slice images are used, and it is difficult to assert that the results of the research were obtained by an accurate quantification of the overall three-dimensional (3D) lungs.
The development of medical image technology, particularly the development of 3D CT images, enables small sub-millimeter structures to be observed in a living body. There has been rapid advancement not only in spatial resolution but also in temporal resolution. However, it is difficult to quantify small blood vessels based on 3D CT images via an automated algorithm due to the complicated morphological structures of blood vessels, for example, a densely populated distribution, proximately intersecting cases, other parallel neighbor blood vessels, etc. In particular, there has not been a successful attempt to classify small blood vessels into arteries and veins and then quantify them based on 3D CT images via an automated algorithm.
It is not easy to segment and/or classify pulmonary arteries and pulmonary veins. Since pulmonary vessels are densely distributed across the lungs and the morphological characteristics (radii, branching patterns, etc.) thereof vary from person to person, it is not easy to distinguish the blood vessels even when the pulmonary vessels have been segmented. Furthermore, since pulmonary arteries and pulmonary veins intersect each other, they are seen as overlapping each other in a 3D image, such as a CT image. Related technology includes a technology disclosed in the paper by T. Buelow, R. Wiemker, T. Blaffert, C. Lorenz, S. Renisch, “Automatic extraction of the pulmonary artery tree from multi-slice CT data,” Medical Imaging 2005: Physiology, Function, and Structure from Medical Images. Proceedings of the SPIE, 5746, pp. 730-740, Apr. 2005.”
Therefore, there is a need for developing a method for distinguishing between pulmonary arteries and veins via an automated algorithm, three-dimensional visualization of arteries and vein in an organ and quantifying the blood vessels, including diameters and lengths, throughout the organ based on the state of the blood vessels.